Biology of Disease

Other techniques for investigating thyroid function include administration of

isotopes, such as 99mTc-pertechnetate, and determining their distribution using

a camera that detects F radiation. This technique distinguishes between active

and inactive thyroid nodules and can distinguish between Grave’s disease,

multinodular goiter or an adenoma affecting the thyroid gland. A thyroid

biopsy involves aspirating tissue from the affected region of the thyroid using

a syringe and fine needle. The collected cells are examined microscopically

for evidence of thyroid nodules. Often thyroid disease has an autoimmune

basis and measurement of antibodies can aid diagnosis. Antiperoxidase and

antithyroglobulin antibodies are found in patients affected by Hashimoto’s

thyroiditis and often in those with Grave’s disease. However, the detection of

antibodies is not always diagnostic, as low levels of these antibodies can occur

in older people who are euthyroid.

The management of hyperthyroidism includes using antithyroid drugs, for

example, carbimazole. This is useful in young patients and acts by reducing

the production of thyroid hormones. Other forms of treatment include

radioiodine therapy with^131 I, although this is normally used in older patients,

and partial or complete surgical removal of the thyroid gland (thyroidectomy).

Some patients develop hypothyroidism, often as a consequence of treatment,

and may have to be placed on thyroxine therapy. In this regard it is important

to monitor TSH levels to detect developing hypothyroidism. Management

of hypothyroidism involves replacement therapy with thyroxine, often for

life. Thyroxine is readily available, safe and inexpensive. The treatment is

monitored at regular intervals by measurement of serum concentrations of

TSH to ensure they are kept within its reference range.

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1.0

0

5

10

15

20

25

30

35

40

Serum [TSH] / mU dm

-3

Hypothyroid (exaggerated response)

Normal response

Hypothalamic (delayed response)

Hyperthyroid (no response)

0.5

Time / h

0.0

TRH administered

Figure 7.21 Potential results from a TRH test. See

text for details.